Solid electrolyte and preparation method and application thereof

Abstract

The invention belongs to the technical field of lithium batteries, and relates to a solid electrolyte and a preparation method and application thereof. The solid electrolyte comprises an inorganic filler, a polymer matrix and a lithium salt, the chemical general formula of the inorganic filler is LiRxY (1-x) SiO4, and x is more than 0 and less than 0.1; r comprises at least one of Ce, Sc, Mn, Fe, Pb, Bi, Zr, La, Sm, Ga, Gd, Dy, Tm and Lu. In the solid electrolyte provided by the invention, the adopted inorganic filler LiRxY1-xSiO4 has a large number of oxygen vacancies, so that lithium salt dissociation can be promoted, and the concentration of free lithium ions can be increased. Meanwhile, the filler can also effectively reduce the crystallinity of a polymer matrix, so that the available region of ion migration is expanded, the prepared solid electrolyte is ensured to have relatively high ionic conductivity and a relatively wide electrochemical window, and the solid electrolyte has a good application prospect in the field of lithium batteries.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, and in particular to a solid electrolyte, its preparation method, and its application. Background Technology

[0002] Traditional liquid lithium batteries generally use flammable and leak-prone organic electrolytes, posing safety hazards such as thermal runaway. Solid electrolytes, as an important alternative, not only eliminate the main flammable components inside the battery by using solid materials to replace liquid electrolytes, significantly improving the battery's intrinsic safety, but also effectively suppress separator puncture caused by lithium dendrite growth and the resulting internal short circuits.

[0003] Currently, solid electrolytes mainly include polymer solid electrolytes, oxide solid electrolytes, and sulfide solid electrolytes. Among them, polymer solid electrolytes use high-molecular polymers as the matrix and introduce lithium salts to construct ion transport channels. However, these electrolytes generally suffer from low ionic conductivity at room temperature, limiting their overall electrochemical performance; at the same time, their mechanical strength is also insufficient for practical applications. Polymer-based electrolytes, represented by polyvinylidene fluoride (PVDF), have high crystallinity at room temperature and lack effective ion binding sites, resulting in insufficient ion conduction capacity. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a solid electrolyte, its preparation method and application.

[0005] In a first aspect, the present invention provides a solid electrolyte comprising an inorganic filler, a polymer matrix, and a lithium salt, wherein the inorganic filler has the general chemical formula: LiR x Y 1-x SiO4, wherein 0 < x < 0.1; wherein R includes at least one of Ce, Sc, Mn, Fe, Pb, Bi, Zr, La, Sm, Ga, Gd, Dy, Tm and Lu.

[0006] The inorganic filler LiR used in the solid electrolyte provided by this invention x Y 1-x SiO4 possesses a large number of oxygen vacancies, which can promote lithium salt dissociation and increase the concentration of free lithium ions. Simultaneously, this filler can effectively reduce the crystallinity of the polymer matrix, thereby expanding the usable area for ion migration and ensuring that the prepared solid electrolyte has high ionic conductivity and a wide electrochemical window.

[0007] Preferably, 0.01 ≤ x ≤ 0.03. As some alternative examples of x, x can be 0.01, 0.012, 0.015, 0.018, 0.02, 0.022, 0.025, 0.028, 0.03, etc. It is understood that x can also be chosen in other numerical ranges from 0.01 to 0.03.

[0008] More preferably, x = 0.02.

[0009] Preferably, R is Ce.

[0010] Preferably, the mass of the inorganic filler is 5-50% of the mass of the polymer matrix, and the mass ratio of the polymer matrix to the lithium salt is (1-5):1.

[0011] More preferably, the mass of the inorganic filler is 20% of the mass of the polymer matrix, and the mass ratio of the polymer matrix to the lithium salt is 2:1.

[0012] The polymer matrix includes at least one of polyvinylidene fluoride, polyacrylonitrile, and polyethylene oxide.

[0013] The lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), and lithium perchlorate (LiClO4).

[0014] In a second aspect, the present invention provides a method for preparing the above-mentioned solid electrolyte, comprising the following steps: S1. Weigh each raw material according to the stoichiometric ratio, and after secondary sintering and ball milling, obtain the inorganic filler; S2. The polymer matrix and lithium salt are dissolved in an organic solvent and heated. Then, inorganic filler is added, and the mixture is subjected to ultrasonication, stirring, casting, and drying to obtain the solid electrolyte.

[0015] Preferably, in step S1, the temperature of the first sintering in the secondary sintering is 700-900℃ and the time is 4-8h.

[0016] Preferably, in step S1, the second sintering temperature is 1000-1200℃ and the time is 5-15h.

[0017] Preferably, in step S1, the secondary sintering is carried out in a protective gas atmosphere.

[0018] Preferably, the protective gas is 5% hydrogen and 95% argon.

[0019] Preferably, in step S1, the ball mill rotates at a speed of 800-1500 rpm for 0.5-12 hours, and the ball-to-material ratio is (1-20):1.

[0020] Preferably, in step S1, the ball mill rotates at 1100-1300 rpm for 0.5-2 hours, and the ball-to-material ratio is (1-5):1.

[0021] Preferably, in step S2, the mass-to-volume ratio of the polymer matrix to the organic solvent is 1 g: (10-20) mL.

[0022] Preferably, in step S2, the organic solvent includes at least one of tetrahydrofuran, acetone, N,N-dimethylformamide, N,N-dimethylacetamide, and dichloroethane.

[0023] Preferably, in step S2, the heating temperature is 45-65℃ and the heating time is 8-24h.

[0024] Preferably, in step S2, the ultrasound duration is 10-60 minutes and the power is 100-500W.

[0025] Preferably, in step S2, the ultrasound duration is 20-40 minutes and the power is 200-400W.

[0026] Preferably, in step S2, the stirring time is 8-24 hours.

[0027] Preferably, in step S2, the drying temperature is 50-70°C and the time is 8-24 hours.

[0028] The solid electrolyte prepared by the method of the present invention has high ionic conductivity.

[0029] In a third aspect, the present invention provides a solid-state battery comprising the above-described solid electrolyte.

[0030] In a fourth aspect, the present invention provides an electrical device comprising the aforementioned solid-state battery.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows: The inorganic filler LiR used in the solid electrolyte provided by this invention x Y 1-x SiO4 possesses a large number of oxygen vacancies, which can promote lithium salt dissociation and increase the concentration of free lithium ions. Simultaneously, this filler can effectively reduce the crystallinity of the polymer matrix, thereby expanding the usable area for ion migration and ensuring that the prepared solid electrolyte has high ionic conductivity and a wide electrochemical window, showing promising application prospects in the field of lithium batteries. Attached Figure Description

[0032] Figure 1 For LiCe 0.02 Y 0.98 XRD pattern of SiO4 (inorganic filler A2), R wp =3.2%.

[0033] Figure 2 The image shows the electrochemical impedance spectroscopy of the battery assembled with the solid electrolyte in Example 3.

[0034] Figure 3 The image shows a linear sweep voltammetry curve of the battery assembled with the solid electrolyte in Example 3.

[0035] Figure 4 Cycling diagrams of the batteries assembled with solid electrolytes in Example 3 and Comparative Examples 1-2.

[0036] Figure 5 This is a lithium deposition stripping diagram of the battery assembled with a solid electrolyte in Example 3.

[0037] Figure 6 Tensile stress-strain diagrams of the solid electrolyte membranes of Example 3 and Comparative Example 1. Detailed Implementation

[0038] The following detailed embodiments further illustrate the content of the present invention. These embodiments do not constitute a limitation on the scope of protection of the present invention. Non-essential modifications and adjustments made by others based on the concept of the present invention still fall within the scope of protection of the present invention. The raw materials, reagents, or devices used in the embodiments are all available from conventional commercial sources or can be obtained through existing technical methods. Unless otherwise specified, the experimental or testing methods are conventional methods in the art.

[0039] Composition and preparation of inorganic fillers The compositions of inorganic packings A1-A3 and inorganic packing B1 are shown in Table 1. The inorganic packings are prepared through the following steps: S1. Weigh the raw materials Li2CO3, Y2O3, SiO2 and CeF3 according to the stoichiometric ratio, grind them evenly, place them in a tube furnace at 820℃, introduce a reducing mixed atmosphere (5% H2 and 95% Ar), carry out a high-temperature solid-phase reaction for 6 hours, and then cool to room temperature to obtain the powder after one sintering.

[0040] S2. After grinding the powder after the first sintering, a reducing mixed atmosphere (5% H2 and 95% Ar) is introduced into a tube furnace at 1100℃ for a high-temperature solid-phase reaction for 10 hours. Then, the powder is cooled to room temperature to obtain the powder after the second sintering.

[0041] S3. The powder after secondary sintering is ball-milled at a speed of 1200 r / min and a ball-to-material ratio of 1:1 for 1 h to obtain the inorganic filler.

[0042] Table 1 Inorganic filler A2 was used for XRD testing, and the results are as follows: Figure 1 As shown.

[0043] Example 1 This embodiment provides a solid electrolyte, which is prepared through the following steps: Weigh 1g PVDF and 0.5g LiTFSI, add them to 15mL DMF solution, heat at 55℃ for 12h, then add 0.2g LiCe. 0.01 Y 0.99 SiO4 (inorganic filler A1) was ultrasonically dispersed for 30 minutes (power 300W) and stirred for 12 hours. The film was then formed by casting and vacuum dried at 60°C for 12 hours before being sliced ​​to obtain a solid electrolyte membrane.

[0044] Example 2 Weigh 1g PVDF and 0.5g LiTFSI, add them to 15mL DMF solution, heat at 55℃ for 12h, then add 0.1g LiCe. 0.02 Y 0.98 SiO4 (inorganic filler A2) was ultrasonically dispersed for 30 minutes and stirred for 12 hours, then cast into a film by casting, and vacuum dried at 60°C for 12 hours to obtain a solid electrolyte membrane.

[0045] Example 3 The only difference from Example 2 is the addition of 0.2g LiCe. 0.02 Y 0.98 The SiO4 (inorganic filler A2) and other components and preparation steps are the same as in Example 2.

[0046] Example 4 The only difference from Example 3 is the addition of 0.3g LiCe. 0.02 Y 0.98 The SiO4 (inorganic filler A2) and other components and preparation steps are the same as in Example 3.

[0047] Example 5 The only difference from Example 3 is the addition of 0.4g LiCe. 0.02 Y 0.98 The SiO4 (inorganic filler A2) and other components and preparation steps are the same as in Example 3.

[0048] Example 6 The only difference from Example 3 is that the 0.5g LiTFSI in Example 2 is replaced with 0.5g LiFSI, while the other components and preparation steps are the same as in Example 3.

[0049] Example 7 The only difference from Example 3 is that the 15 mL DMF (N,N-dimethylformamide) solution in Example 2 is replaced with 15 mL DMAc (N,N-dimethylacetamide), while the other components and preparation steps are the same as in Example 3.

[0050] Example 8 The only difference from Example 3 is that 1g of PVDF in Example 2 is replaced with 1g of PAN, while the other components and preparation steps are the same as in Example 3.

[0051] Example 9 The only difference from Example 3 is that 1g of PVDF in Example 2 is replaced with 1g of PEO, while the other components and preparation steps are the same as in Example 3.

[0052] Example 10 Weigh 1g PVDF and 0.5g LiTFSI, add them to 15mL DMF solution, heat at 55℃ for 12h, then add 0.2g LiCe. 0.03 Y 0.97 SiO4 (inorganic filler A3) was ultrasonically dispersed for 30 minutes and stirred for 12 hours, then cast into a film by casting, and vacuum dried at 60°C for 12 hours to obtain a solid electrolyte membrane.

[0053] Comparative Example 1 This comparative example provides a solid electrolyte, which is prepared by the following steps: Weigh 1g PVDF and 0.5g LiTFSI, add them to 15mL DMF solution, heat at 55℃ for 12h without adding inorganic filler, stir for 12h, and then prepare a film by casting. After vacuum drying at 60℃ for 12h, slice the film to obtain a solid electrolyte membrane.

[0054] Comparative Example 2 The only difference from Example 3 is that the 0.2g LiCe from Example 3 is used instead. 0.02 Y 0.98 SiO4 (inorganic filler A2) was replaced with 0.2g LiYSiO4 (inorganic filler B1), and the remaining components and preparation steps were the same as in Example 3.

[0055] Comparative Example 3 The difference from Example 3 is that ultrasonic dispersion is not performed during the preparation process, while the remaining components and preparation steps are the same as in Example 3.

[0056] The solid electrolytes of the examples and comparative examples were subjected to performance tests, and the test methods included: (1) Lithium-ion conductivity: The solid electrolytes obtained in Examples 1-10 and Comparative Examples 1-3 were assembled into stainless steel | electrolyte film | stainless steel coin cells, and their electrochemical impedance spectroscopy was tested to obtain the corresponding ionic conductivity values. The test results are shown in Table 2. Among them, the electrochemical impedance spectroscopy of the solid lithium battery assembled with the solid electrolyte in Example 3 is shown in Table 2. Figure 2 As shown.

[0057] (2) Stability Test: After assembling the stainless steel sheet, the solid electrolytes obtained in Examples 1-10 and Comparative Examples 1-3, and the lithium sheet into a battery in sequence, a linear sweep voltammetry (LSV) test was performed. The test results are shown in Table 2. The LSV curve of the solid lithium battery assembled with the solid electrolyte of Example 3 is shown in Table 2. Figure 3 As shown.

[0058] (3) Capacity test: The solid electrolytes obtained in Example 3 and Comparative Example 1 were assembled into batteries with lithium iron phosphate cathodes. The capacity retention rate after 400 cycles at 1 C and 25 °C was tested. The results are as follows: Figure 4 As shown.

[0059] The results showed that the specific capacity of Example 3 in the first cycle was 137.9 mAh / g, and the specific capacity after 400 cycles was 116.2 mAh / g, with a capacity retention rate of 84% after 400 cycles. In contrast, the specific capacity of Comparative Example 1 in the first cycle was 130 mAh / g, but after 200 cycles it was only 60.3 mAh / g, with a capacity retention rate of 46%. Furthermore, the specific capacity of Comparative Example 2 in the first cycle was 131.8 mAh / g, but the capacity dropped sharply after 250 cycles, reaching only 61.7 mAh / g after 300 cycles, with a capacity retention rate of only 47%.

[0060] (4) Lithium cycling deposition and stripping test: The electrolyte obtained in Example 3 was assembled into a lithium metal|electrolyte film|lithium metal coin cell for lithium cycling deposition and stripping analysis at room temperature. The deposition and stripping current was 0.15 mA / cm. 2 The result is as follows Figure 5 As shown, the battery assembled with the solid electrolyte prepared in Example 3 exhibits a stable lithium deposition stripping overpotential plateau under the above test conditions, which can last for 2500 hours. This indicates that the solid electrolyte has good stability for metallic lithium and can be applied to solid-state batteries.

[0061] (5) Mechanical strength test: To evaluate the mechanical properties of the solid electrolyte, tensile tests were conducted on the solid electrolyte membranes obtained in Example 3 and Comparative Example 1 using an electronic universal testing machine at a constant rate of 50 mm / min. The stress-strain relationship was determined, and the results are as follows: Figure 6 As shown.

[0062] The results show that Comparative Example 1 has a tensile strength of 4.5 MPa and a tensile strength at break of 29%, exhibiting low mechanical properties and being prone to brittle fracture under stress. In contrast, Example 3 has a tensile strength of 6.7 MPa (an increase of approximately 49%) and a tensile strength at break of 42% (an increase of approximately 45%), demonstrating superior mechanical strength, which means it can more effectively suppress lithium dendrite growth.

[0063] Table 2 The results show that the ionic conductivity of the solid electrolytes prepared in Examples 1-10 can reach 2.2 × 10⁻⁶. -4 -6.2×10 - 4 The electrochemical window reaches 4.6-5 V, and in particular, the solid electrolyte prepared in Example 3 has an ionic conductivity as high as 6.2 × 10⁻⁶ S / cm. -4 With a conductivity of S / cm and an electrochemical window as high as 5V, the solid electrolyte provided by this invention can achieve both high ionic conductivity and excellent electrochemical stability. Furthermore, the solid electrolytes prepared in Comparative Examples 1-3 exhibit significantly lower ionic conductivity than those in Examples 1-10, further demonstrating the improved ionic conductivity performance of the solid electrolyte provided by this invention.

Claims

1. A solid state electrolyte, characterized by, The solid-state electrolyte comprises an inorganic filler, a polymer matrix, and a lithium salt, the inorganic filler has a general chemical formula of: LiR x Y 1-x SiO4, wherein 0 < x < 0.1; The R includes at least one of Ce, Sc, Mn, Fe, Pb, Bi, Zr, La, Sm, Ga, Gd, Dy, Tm and Lu.

2. The solid-state electrolyte of claim 1, wherein, 0.01≤x≤0.03, and the R is Ce.

3. The solid-state electrolyte of claim 1, wherein, The mass of the inorganic filler is 5-50% of the mass of the polymer matrix, and the mass ratio of the polymer matrix to the lithium salt is (1-5):

1.

4. The solid state electrolyte of claim 1, wherein, The mass of the inorganic filler is 20% of the mass of the polymer matrix, and the mass ratio of the polymer matrix to the lithium salt is 2:

1.

5. The solid state electrolyte of claim 1, wherein, The polymer matrix includes at least one of polyvinylidene fluoride, polyacrylonitrile and polyethylene oxide.

6. A method of preparing a solid-state electrolyte as claimed in any one of claims 1-5, characterized in that, The method comprises the following steps: S1. The raw materials are weighed according to the stoichiometric ratio, and the inorganic filler is obtained after secondary sintering and ball milling; S2. The polymer matrix and the lithium salt are dissolved in an organic solvent and heated, and then the inorganic filler is added, and the solid-state electrolyte is obtained after ultrasonic treatment, stirring, film casting and drying.

7. The method of claim 6, wherein, In step S1, at least one of the following features (1) to (4) is included: (1) In the secondary sintering, the temperature of the first sintering is 700-900℃, and the time is 4-8h; (2) In the secondary sintering, the temperature of the second sintering is 1000-1200℃, and the time is 5-15h; (3) The secondary sintering is carried out in a protective gas atmosphere; (4) The rotation speed of the ball milling is 800-1500rpm, the time is 0.5-12h, and the ball-to-material ratio is (1-20):

1.

8. The method of claim 6, wherein, In step S2, at least one of the following features (1) to (6) is included: (1) The mass-to-volume ratio of the polymer matrix to the organic solvent is 1g:(10-20)mL; (2) The organic solvent includes at least one of tetrahydrofuran, acetone, N,N-dimethylformamide, N,N-dimethylacetamide and dichloroethane; (3) The heating temperature is 45-65℃, and the heating time is 8-24h; (4) The ultrasonic treatment time is 10-60min, and the power is 100-500W; (5) The stirring time is 8-24h; (6) The drying temperature is 50-70℃, and the time is 8-24h.

9. A solid state battery, characterized by The solid-state electrolyte as claimed in any one of claims 1-5.

10. An electrical device, characterized by The solid-state battery as claimed in claim 9.

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